1. Field of the Invention
The disclosed method relates generally to wireless network communication techniques and, in particular, to a method and system for network-wide broadcast via hopping between nodes equipped with directional antennas, with rebroadcast restricted based on node location and yawing position.
2. Background of the Related Art
Conventional wind farms have multiple wind turbines. Each turbine typically has a nacelle located at an upper portion thereof, onto which turbine blades are rotatably connected. Each nacelle of each wind turbine in the wind farm will yaw about a vertical axis, to position the nacelle and turbine blades into the wind for maximum power production. See U.S. Publ. No. 2005/0196280 A1 to Gonzalez et al. and U.S. Publ. No. 2010/0109327 A1 to Nielson et al., the contents of which are incorporated herein by reference.
The need for each of the multiple turbines in the wind farm to wirelessly communicate is well recognized, for reasons that include but are not limited to efficient and reliable propagation of aircraft approach alert signals to activate an anti-collision warning light located on each nacelle.
Wireless communication protocols are well known. Conventional protocols include a random access protocol, such as Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). See IEEE 802.11 Wireless Local Area Network (“WLAN”) standard and U.S. Pat. Nos. 5,761,431 and 6,680,950, the contents of which are incorporated herein by reference.
In such conventional methods, a same wireless communication channel is typically utilized for all nodes in a network, avoiding the need to coordinate between the transmitter and receiver of a link to select a communication channel. A multi-hop wireless routing is needed when source and destination nodes are not connected by a direct link. Multi-hop routing is typically achieved by relaying packets over multiple links, i.e. hops that involve intermediate nodes. Such routing can be unicast or broadcast.
For unicast routing, a source node sends the packet to a specific destination node located one or more hops away. A routing protocol at the network layer determines a next hop node to forward the packet via a link layer transmission.
For broadcast routing, a source node sends the packet to all nodes in the network. Broadcast routing, sometimes referred to ‘flooding’, is typically used to distribute network wide control or management information, as described in U.S. Pat. No. 7,369,512, the contents of which are incorporated herein by reference.
Omni-directional antennas are typically used to facilitate flooding since all neighboring nodes will receive the packet using a single link layer broadcast and will relay the packet by link layer broadcast. For example, in a naïve flooding broadcast method a source node broadcasts a packet via a single link layer broadcast. Any other node, upon receiving a packet for the first time, rebroadcasts the packet via a single link layer broadcast. When a node receives the rebroadcast of same packet, a duplicate, i.e. rebroadcast, packet is ignored to prevent endless rebroadcast throughout the network.
To recognize duplicate packets, a unique signature is typically provided in a packet header. The originating or source node inserts the signature in the packet header. In this example method of naïve flooding, every node in a network having ‘N’ number of nodes will transmit via a broadcast transmission at the link layer each unique packet only once, resulting in N number of transmissions of each packet.
However, naïve flooding is inefficient since nodes having links that are linked to more than one other node will receive the same packet more than once. Accordingly, to improve network efficiency and to reduce packet loss due to packet collisions in a shared wireless channel, there is a need to achieve network-wide broadcast utilizing less than N packet transmissions.
For wireless communication between wind farm turbines, it has been proposed to use directional antennas instead of omni-directional antennas. In a directional antenna, wireless communication is restricted to a sector for reasons that include reduction of interference and providing longer transmission range. Multiple directional antennas with non-overlapping sectors are used in a node to cover the entire circle. However, conventional use of directional antennas fails to account for yawing of the wind turbine as they also rotate along with the node itself. Conventional systems also fail to provide a method to reduce congestion of a shared transmission channel as each antenna broadcasts the packet once to implement flooding. Thus, in a network with N nodes and k directional antennas per node, with k being equal to or greater than two, N*k packet transmission are required, resulting in network congestion and packet collisions.